The present invention relates to a method of producing a gas barrier film making use of capacitively coupled plasma-enhanced chemical vapor deposition, and more specifically relates to a gas barrier film production method capable of producing a gas barrier film having good gas barrier properties using a less heat-resistant substrate.
Gas barrier films having a silicon nitride layer deposited on the surface of a resin (plastic) film are known as gas (water vapor) barrier films employed in various apparatuses and optical devices which are required to be moisture-proof.
Capacitively coupled plasma-enhanced chemical vapor deposition (hereinafter abbreviated as “CCP-CVD”) is a known process for depositing a silicon nitride layer.
As is well known, CCP-CVD is a technique in which a material gas is supplied between a pair of electrodes used, and a voltage is applied to generate plasma, which causes the material gas to dissociate and ionize to generate radicals and ions, thus performing film deposition on the surface of an object disposed between the electrodes for treatment.
CCP-CVD is advantageous in that, by supplying the material gas through the electrodes, the material gas can be uniformly supplied to the whole film-forming area (gas is easily made uniform) even in the case where the electrodes have an increased surface area, and hence this technique can be easily applied to a substrate having a large surface area.
For example, JP 2005-342975 A discloses a transparent gas barrier film which has a silicon nitride layer having an N/Si elemental ratio of 0.8 to 1.4 and a film density of 2.1 to 3 g/cm2.
In Examples of JP 2005-342975 A, a silicon nitride layer is formed by CCP-CVD on a polyethersulfone film as a substrate using a material gas including silane gas, ammonia gas and hydrogen gas under the conditions of a substrate temperature of 150° C., a silane gas flow rate of 2 to 20 sccm, a power applied of 300 W, and a film deposition pressure of 10 Pa, thus producing a gas barrier film.
As described in JP 2005-342975 A, a resin film is used for the substrate of a gas barrier film.
JP 2005-342975 A uses a polyethersulfone film for the substrate and deposits a silicon nitrate layer at a substrate temperature of 150° C., but it is difficult to deposit a silicon nitride layer on a less heat-resistant resin film such as an inexpensive polyethylene terephthalate (PET) film at the substrate temperature of 150° C.
Film deposition at a lower temperature enables a silicon nitride layer to be deposited on a less heat-resistant resin film such as a PET film. However, gas barrier films obtained by film deposition at such a low temperature very often have no desired performance.
In addition, a film deposition pressure of 10 Pa requires a sophisticated film deposition device, and particularly in cases where improvement of the productivity, that is, improvement of the flow rate of a material gas is desired, involves a considerable increase in device cost.